1. Field of the Invention
The invention relates to a process for degassing a paper stock suspension using a vacuum, in which the suspension is separated into partial streams and is sprayed into a degassing chamber that is influenced by a vacuum. The gas separated here, e.g., air, is suctioned out of the degassing chamber.
Gas bubbles in the stock suspension worsen the paper quality and enhance undesired pulsing. Therefore, it is necessary to degas, in particular in fast running paper machines that produce sorts of paper, e.g., newspapers, LWC, coating prints, etc., made with suspensions using raw materials such as mechanical wood pulp, deinked sorted used paper, or pulp. The gasses contained therein usually include of air. In general, the degassing occurs in that the suspension is sprayed and exposed to a vacuum. This vacuum is set as high as possible, preferably up to the pressure of steam.
2. Discussion of Background Information
A process for degassing a paper stock suspension is known from DE 41 06 140 A1 in which the suspension is divided into a number of partial streams and then is sprayed in a degassing chamber. With the aid of the high number of very small partial streams suggested there, as good a degassing as possible is to occur. While such a process does have an acceptable effectiveness, it is expensive in its use of energy as well as in relation to the amount of machinery.
The present invention provides a degassing process that further increases the degassing effectiveness and reduces the expense necessary therefor, in particular the use of energy.
The present invention provides a degassing process similar in general to the above-described process that further includes exposing the fibrous paper suspension to the vacuum necessary for the degassing for a duration of at least 10 seconds.
With the aid of the new process, the paper stock suspension to be degassed is kept under the influence of a comparatively strong vacuum, in particular for a duration whose length is several times larger than the processes known up to now. Special phenomena are put into consideration that are obviously connected to the nature of suspended paper fibers containing gas. Surprisingly, it is particularly advantageous when the gas, diluted or adhering to the fibers, is given more time to separate or detach and form a gas bubble. The degassing effectiveness can be increased in this manner, which leads to, e.g., a lowering of the requirements of the adjacent degassing in the degassing chamber. The separation into partial streams and sprays in the degassing chamber is expensive, both in the devices and the energy consumption. If, however, the fibrous stock suspension has previously been exposed to a vacuum, it is possible for either some of the gasses to already be removed or at least pulled far enough out of the fibrous connection that the subsequent degassing in the degassing chamber is facilitated. Extending the vacuum duration can also occur after the spraying, e.g., in a post-degassing chamber.
An additional advantage can be achieved in creating tangential currents by correlating guidance of the currents in the pre-gassing chamber, which even better expel the already separating gas bubbles out of the fibrous web. For this purpose, integrated current devices can be used advantageously that are known, e.g., from static mixers.
In the design of the device forming the pre-degassing chamber or the post-degassing chamber, attention must be paid to allowing the necessary lag time for all components of the fibrous stock suspension and, thus, avoiding undesired currents due to shorts or mixings. The measures necessary therefor are known to one trained in the art. They can be designed in such a way that they aid in the above-mentioned lateral currents in the suspension as well.
Another improvement presents itself when the partial streams in the degassing chamber are directed downwardly, since then they cause a smaller loss of pressure in the device creating the partial streams, e.g., a perforated metal sheet. Based on a maximal vacuum in the degassing chamber (the steam pressure) this leads to a higher vacuum in the pre-degassing.
The instant invention is directed to a process for degassing a flowing fibrous paper suspension. The process includes separating the suspension into partial streams, spraying the partial streams into a degassing chamber under vacuum, and exposing the suspension to the degassing vacuum for at least 10 seconds. In this manner, gas within the suspension is separated from the suspension. The process also includes suctioning the separated gas out of the degassing chamber.
In accordance with a feature of the present invention, the gas may include air.
According to another feature oft he instant invention, the suspension is exposed to the degassing vacuum for at least 30 seconds.
An absolute pressure in the degassing chamber may be comparable to a steam pressure of the fibrous paper suspension at the prevailing temperature. The degassing pressure can be equivalent to the steam pressure of the fibrous paper suspension during the entire degassing time.
According to still another feature of the invention, the separating into and spraying of partial streams may be performed with a loss of pressure in the suspension of no more than about 0.4 bar. Further, the loss of pressure due to the separating into and spraying of partial streams can be no more than about 0.15 bar.
In accordance with a further feature of the present invention, the partial streams can be directed downwardly. Alternatively, the partial streams may be directed upwardly.
Prior to separating the suspension into partial streams, the fibrous paper suspension can be exposed to a vacuum sufficient for degassing a pre-degassing chamber. An absolute pressure in the pre-degassing chamber may be no more than about 0.2 bar. The fibrous paper suspension can be guided in the pre-degassing chamber such that tangential currents develop to facilitate separation of the gas bubbles from the suspension. Moreover, the process can further include collecting some of the separated gas in the pre-degassing chamber, and suctioning at least part of the collected gas out of the pre-degassing chamber. The fibrous paper suspension may be guided downwardly from the pre-degassing chamber to the degassing chamber via a falling distance with a height of at least about 1 m. The pre-degassing chamber can include a horizontally positioned oblong container.
After the degassing chamber, the fibrous paper suspension can be exposed to a vacuum sufficient for degassing a post-degassing chamber. The vacuum in the post-degassing chamber may be equivalent to the degassing vacuum.
Further, the present invention is directed to a process for degassing a fibrous material suspension in an apparatus that includes a degassing chamber and an element arranged at an inlet of the degassing chamber for dividing the suspension into a plurality of partial streams. The process includes exposing the suspension in the apparatus to a vacuum sufficient to degas the suspension for a duration of at least 10 seconds, such that gas within the suspension in at least the degassing chamber is separated from the suspension. The process also includes suctioning at least a portion of the separated gas out of the degassing chamber.
In accordance with a feature of the invention, the apparatus can further include a pre-degassing chamber arranged upstream from the degassing chamber, relative to a suspension flow direction, and the pre-degassing chamber can be under a vacuum sufficient for degassing. Further, the exposing of the suspension to the vacuum further may include forming tangential currents in the suspension in the pre-degassing chamber to remove gas in the suspension from the suspension, and suctioning at least a portion of the removed gas out of the pre-degassing chamber. The degassing chamber and the pre-degassing chamber can be arranged such that the suspension falls at least 1 meter from the pre-degassing chamber to the degassing chamber. The suspension may be directed downwardly through the element, or the suspension may be directed upwardly through the element.
In accordance with yet another feature of the present invention, the apparatus can further include a post-degassing chamber arranged downstream from the degassing chamber, relative to a suspension flow direction, and the exposing of the suspension to the vacuum may include exposing the suspension to a vacuum sufficient to degas the suspension for the duration to separate the gas within the suspension in the degassing chamber and in the post-degassing chamber from the suspension, and suctioning at least a portion of the separated gas out of the degassing chamber. The degassing of the suspension in the post-degassing chamber can include forming tangential currents in the suspension in the pre-degassing chamber.
The present invention is directed to an apparatus for degassing a flowing fibrous paper suspension. The apparatus includes a degassing chamber structured to subject the suspension to a vacuum sufficient for degassing, an element arranged at an inlet of said degassing chamber for dividing the suspension into a plurality of partial streams, and a suction device for removing separated gas from said degassing chamber. The apparatus is structured and arranged so that the suspension is subjected to the degassing vacuum for a duration of at least 10 seconds.
In accordance with a feature of the instant invention, the apparatus can further include a pre-degassing chamber arranged upstream from the degassing chamber, relative to a suspension flow direction. The pre-degassing chamber can be under a vacuum sufficient for degassing, and the pre-degassing chamber and the degassing chamber may be arranged such that the suspension is subject to the degassing vacuum in said chambers for the duration. Further, a suction device can be provided for removing separated gas from the pre-degassing chamber.
According to yet another feature of the present invention, the apparatus can further include a post-degassing chamber arranged downstream from the degassing chamber, relative to a suspension flow direction. The post-degassing chamber can be under a vacuum sufficient for degassing, and the post-degassing chamber and the degassing chamber may be arranged such that the suspension is subject to the degassing vacuum in said chambers for the duration. Further, a suction device can be provided for removing separated gas from said post-degassing chamber.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.